I have a constant heartbeat hum in my ear that is louder at night? What is it and how to treat?

Carotid stenosis. Need to be checked for narrowing of your carotid artery. Usually a simple ultrasound.
Carotid bruit. Occasionally this may be the bruit from a carotid stenosis. I would recommend that you should have a carotid ultrasound to see if there is any carotid disease.